Background. Neuroticism has been shown to increase the risk of depression whereas extraversion is associated with a reduction of risk. These personality traits play a central role in aetiological theories of affective disorder but their role in schizophrenia is unclear. In this study, the risk for schizophrenia associated with neuroticism and extraversion was examined and quantified.

Methods. Neuroticism and extraversion rated at the age of 16 years were examined in relation to adult schizophrenia in a national birth cohort of 5362 individuals.

Results. Neuroticism increased the risk of later schizophrenia independent of the level of affective symptoms in adult life (odds ratio over three levels: 1·93, 95% CI 1·09–3·43), whereas extraversion reduced the risk (OR: 0·44, 95% CI 0·23–0·84).

Conclusions. Depression and schizophrenia may share personality risk-increasing and risk-reducing factors. Coping styles associated with particular personality traits may determine whether isolated symptoms progress to full-blown illness.